The single crystalline silicon to be used as a raw material for a semiconductor device is manufactured by a pulling method (Czochralski method). In the single crystalline silicon pulling apparatus (manufacturing apparatus), a large amount of argon gas is supplied into a chamber as a shield gas in order to control an oxygen concentration within the silicon crystal and ensure a purity of the single crystalline silicon to be manufactured. The argon gas discharged from the single crystalline silicon pulling apparatus contains methane (CH.sub.4) and other hydrocarbons besides nitrogen (N.sub.2), oxygen (O.sub.2), carbon monoxide (CO), carbon dioxide (CO.sub.2) and the like.
Argon gas (Ar) is present at a concentration of 0.93% in the air and generally purified by cryogenic separation of the air. For this reason, argon gas is relatively expensive. It is therefore desirable that high purity argon gas be recovered from the exhaust gas (argon gas containing impurities) discharged from the single crystalline silicon pulling apparatus by purification, and used again.
Various processes are known to public for purifying the argon gas containing impurities and recovering high purity argon gas. For example, Japanese Patent Application KOKAI publication Nos. 63-189774, 1-230975, 2-272288, and 5-256570 disclose processes for obtaining purified argon gas by removing impurities such as CO, CO.sub.2, and H.sub.2 O by means of adsorption followed by purifying through cryogenic separation or with a catalyst. Furthermore, in Japanese Patent Application KOKAI publication Nos. 2-282682 and 3-39886, and Japanese Patent Application KOKOKU publication Nos. 4-12393 and 5-29834 disclose processes for recovering argon gas including a step of converting impurities such as CO, H.sub.2, and hydrocarbons into H.sub.2 O and CO.sub.2 with a catalyst.
In the processes for purifying argon gas described in the aforementioned publications, hydrocarbons contained as impurities are removed by oxidizing it with a catalyst into H.sub.2 O and CO.sub.2. During this step, an excessive amount of O.sub.2 is added for facilitating the reaction. In other words, O.sub.2 is further added to argon gas, so that a considerable amount of O.sub.2 thus added is left after removal of the hydrocarbons. To remove O.sub.2 from the argon gas, O.sub.2 is reacted with H.sub.2 into H.sub.2 O, and then removed, in a usually employed method. In the oxidation reaction performed with a catalyst, an external heat source is required. Therefore, it may not say that the aforementioned processes are satisfactory methods, in view of energy efficiency.